Household phenomenon observed by Leonardo da Vinci finally explained

August 7, 2018, University of Cambridge
A hydraulic jump is created by water flowing into a sink. Credit: James Niland

An everyday occurrence spotted when we turn on the tap to brush our teeth has baffled engineers for centuries—why does the water splay when it hits the sink before it heads down the plughole?

Famous inventor and painter Leonardo da Vinci documented the phenomenon, now known as a hydraulic , back in the 1500s. Hydraulic jumps are harmless in our household sinks but they can cause violent waves, turbulence and whirlpools in deeper water.

Since the 1820s scientists have believed that hydraulic jumps occur partly as a result of the gravitational pull. But a paper published in the Journal of Fluid Mechanics has disproved this longstanding theory.

Rajesh Bhagat, a Chemical Engineering Ph.D. student at St John's College, University of Cambridge, and first author of the paper, fired jets of water upwards and sideways onto flat surfaces, and witnessed exactly the same hydraulic jumps as those when the water flowed downwards.

But what was causing it? Bhagat suspected they could all affected by the same factors—surface tension and viscosity.

By altering these attributes of the water he was able to accurately predict the size of the hydraulic jumps, regardless of which direction the water was moving—debunking the 200-year-old gravitational theory as the cause of a kitchen sink type hydraulic jump. This kind of hydraulic jump is known as a circular hydraulic jump.

Professor Paul Linden, Director of Research at the Department of Applied Mathematics and Theoretical Physics at the University of Cambridge and an author of the paper, described Bhagat's findings as 'ground breaking'.

He explained: "His experiments and theory show that the surface tension of the liquid is the key to the process and has this has never before been recognised even though the problem was discussed by da Vinci and many others since. This work represents a remarkable achievement in our understanding of the dynamics of thin layers of fluid."

Bhagat predicts that his findings could have wide reaching consequences for industries that have high levels of water consumption.

He said: "Knowing how to manipulate the boundary of a hydraulic jump is very important and now with this theory we can easily extend or reduce the boundary.

"Understanding this process has big implications and could reduce industrial water use dramatically. The new theory is already being used in practical work in the Chemical Engineering department. People can use this to find new ways to clean everything from cars to factory equipment."

Bhagat hopes his research will also be used to find new ways to help us use less in the average household.

Explore further: Scientists train spider to jump on demand to discover secrets of animal movement

More information: Rajesh K. Bhagat et al, On the origin of the circular hydraulic jump in a thin liquid film, Journal of Fluid Mechanics (2018). DOI: 10.1017/jfm.2018.558

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not rated yet Aug 07, 2018
Isn't the effect not a bit similar to the effect of stopping a boat hard in a canal and causing a much larger wave to travel ahead of it as a result, in terms of the sudden increase in wave energy? The velocity of a pebble dropped into water slows abruptly as it sinks before gravity takes it more slowly to the bottom, and the reduced pressure of the channel it gouges into the water behind it combined with the increased pressure of the water it is pushing ahead of it causes that water to be literally sucked up behind it with enough force to create a small fountain ..kind of a combination of two ideas, when Bernoulli is factored in.
Aug 07, 2018
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3 / 5 (2) Aug 08, 2018
Who wrote this garbage?

The cause of hydraulic jumps has been known for the last 150 years, and it isn't gravity. Duh.
Aug 08, 2018
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Captain Skip
not rated yet Aug 14, 2018
funny it never happens in non polar fluids.
Captain Skip
not rated yet Aug 14, 2018
funny it never happens in non polar fluids.

to demonstrate how ignorant and closed minded the physics community is ... when asked if hot water freezes faster than cold water ... no one ever asked if it melts faster. it does.. packing fraction differences based on the speed of the molecules .. haste makes waste.
Aug 14, 2018
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